1. Field of the Invention
The present invention relates to a substrate processing method and a substrate processing apparatus. More specifically, the present invention relates to a substrate processing method and a substrate processing apparatus for processing objects, such as semiconductor wafers or LCD substrates, with a processing liquid and cleaning the objects with a cleaning liquid.
2. Description of the Related Art
Generally, a semiconductor wafer processing apparatus has prevalently been used in fabricating semiconductor devices to remove particles, organic substances, metallic contaminants and/or an oxide film from objects, such as semiconductor wafers, (hereinafter referred to as "wafers") by sequentially conveying the wafers through processing tanks containing processing liquids (chemical liquids) and cleaning tanks containing cleaning liquids (rinsing liquids) to immerse the wafers in the processing liquids and the cleaning liquids and to dry the wafers.
A wafer processing apparatus of this kind comprises processing tanks respectively containing processing liquids (chemical liquids), such as HF+H.sub.2 O (a hydrogen fluoride solution (hereinafter referred to as "HF")), NH.sub.4 OH+H.sub.2 O.sub.2 +H.sub.2 O (an ammonia peroxide solution) and HCl+H.sub.2 O.sub.2 +H.sub.2 O (a hydrochloric acid peroxide solution), cleaning tanks respectively containing cleaning liquids, such as rinsing liquids (pure water), wafer holders, such as wafer boats, for holding a plurality of wafers, for example, fifty wafers, in a vertical attitude, and lifting devices for immersing the wafer boat holding wafers in, and taking out the same from the processing tanks and the cleaning tanks.
The processing tanks, the cleaning tanks and the wafer boats are placed in a downflow atmosphere in which a clean gas, for example, clean air flows down to handle the wafers or the like in a clean atmosphere.
Generally, the wafers or the like made of silicon are provided on their surfaces with an oxide film serving as an insulating film, and a predetermined pattern or the like. When a silicon wafer provided on its surface with an oxide film is processed with a processing liquid, the processing liquid remains on the surface of the silicon wafer because the oxide film is hydrophilic while silicon is hydrophobic. Experiments were conducted to verify this fact. In the experiments, a wafer boat B holding coated silicon wafers Wa coated with an oxide film and bare silicon wafers Wb as shown in FIG. 18A was immersed in a processing liquid, such as HF, contained in a processing tank for processing, and then the wafer boat was taken out of the processing liquid. At this stage, the processing liquid (HF) remained on the surfaces of the coated silicon wafers Wa as shown in FIG. 18B. When the coated silicon wafers Wa and the bear silicon wafers Wb were immersed in a processing liquid or a cleaning liquid for the subsequent process, particles P contained in the processing liquid (HF) remaining on the coated silicon wafers Wa adhered to the surfaces of the coated silicon wafers Wa and therefrom to the surfaces of the adjacent bare silicon wafers Wb as shown in FIG. 18B. As is obvious from the results of the experiments, particles adhere to the surfaces of wafers when silicon wafers coated with an oxide film are processed with a processing liquid and cleaned with a cleaning liquid, and those particles reduces the yield of products.
When etching oxide films formed on the surfaces of wafers W with a processing liquid, such as HF, the wafers W are immersed in the processing liquid (HF) contained in a processing tank, the wafers W are taken out of the processing tank, and the wafers W are carried to a cleaning tank. While the wafers W are thus being carried to the cleaning tank, the processing liquid (HF) remaining on the wafers W flows downward along the surfaces of the wafers W held in a vertical attitude and, consequently, the oxide films coating the wafers W are exposed partly as shown in FIGS. 19A and 19B. Since the etching of the exposed parts of the oxide films is stopped, while the etching of the coated parts of the oxide films continues, the oxide films cannot uniformly be etched, which reduces the yield of products.